Islamically I guess it doesnt matter. However, at the end of the day, if Allah SWT want to keep something from you, then no ultrasound can tell you anything.
I know of one case in our family, where the doc told the mom that she was having a girl, and the mom pinked up in preparation. But it turned out to be a boy in the end. The baby’s position inside the womb can easily cause doctors to mistake a boy for a girl, and vice versa.
At times, even the presence of twins is a surprise not revealed till the actual birth. So it all depends.
But yeah, Islamically, theres nothing that prohibits this.